The paper presents an assessment of the transferable substances amount that is leaking from the packing materials at the food-metallic packing interaction interface by analysing the material balance of the components. The starting point is the theoretical balances of materials. We investigated the transferable materials for rehydrated peas and tomato paste cans. In both cases it was found that an interaction occurs between the organic acids that are found in vegetables as salts and their derivatives, and the metallic structure of the packing material - packaging varnishing system of the can. The real balance of migrated materials gives us an indication concerning the total content of heavy metals accumulated in the cans during the validity period, and allows us to establish precisely a storage period, therefore assuring maximum safety for consumers.